Picrotoxin

Identification

Name

Picrotoxin

Accession Number

DB00466 (APRD00269)

Type

Small Molecule

Groups

Experimental

Description

A noncompetitive antagonist at GABA-A receptors and thus a convulsant. Picrotoxin blocks the gamma-aminobutyric acid-activated chloride ionophore. Although it is most often used as a research tool, it has been used as a CNS stimulant and an antidote in poisoning by CNS depressants, especially the barbiturates. [PubChem]

Pharmacology

Indication

Used internally for relieving respiratory distress. Also for use as an antidote in poisoning by CNS depressants, especially barbiturates.

Pharmacodynamics

Picrotoxin is a toxin obtained from the seeds of the shrub Anamirta cocculus. It is used as a central nervous system stimulant, antidote, convulsant, and GABA (gamma aminobutyric acid) antagonist. It is a noncompetitive antagonist at GABAA receptors and thus a convulsant. Picrotoxin blocks the GABAActivated chloride ionophore. Although it is most often used as a research tool, it has been used as a CNS stimulant and an antidote in poisoning by CNS depressants, especially barbiturates.

Mechanism of action

Picrotoxin antagonizes the GABAA receptor channel directly, which is a ligand-gated ion channel concerned chiefly with the passing of chloride ions across the cell membrane. Therefore picrotoxin prevents Cl- channel permeability and thus promtes an inhibitory influence on the target neuron. Picrotoxin reduces conductance through the channel by reducing not only the opening frequency but also the mean open time. Picrotoxin also antagonizes GABAC receptors (also called GABAA-rho receptors) but the result of this action is not known. The GABAC receptor is also linked to chloride channels, with distinct physiological and pharmacological properties. In contrast to the fast and transient responses elicited from GABAA receptors, GABAC receptors mediate slow and sustained responses.

Oral, mouse: LD50 = 15 mg/kg. In large doses it is a powerful poison, causing unconsciousness, delirium, convulsions, gastro-enteritis and stimulation of the respiratory centre followed by paralysis, from which death sometimes results.

Taxonomy

Description

This compound belongs to the class of organic compounds known as furopyrans. These are organic polycyclic compounds containing a furan ring fused to a pyran ring. Furan is a five-membered aromatic ring with four carbon atoms and one oxygen atom. Pyran a six-membered heterocyclic, non-aromatic ring, made up of five carbon atoms and one oxygen atom and containing two double bonds.